Aspergillus kawachii produces two extracellular beta -glucosidases (EX-1 and EX-2) and one cell-wall-bound beta -glucosidase (CB-1), all of which are derived from the same bglA gene. Extracellular beta -glucosidases (EX-L and EX-2) are stable in the crude solution form, but become unstable in the purified form under moderate conditions (pH 5.0 and 37 degreesC). Purified extracellular beta -glucosidases can bind to a mycelial cell wall fraction, even though these enzymes are released into the medium under solid culture conditions. A. kawachii produces an extracellular soluble polysaccharide (ESP) under solid culture conditions. The addition of purified ESP markedly stabilized the beta -glucosidases over the pH range of 3.0-7.0 and at temperatures below 50 degreesC. ESP directly interacted with the purified extracellular beta -glucosidases but did not affect the K-m values of these enzymes. Moreover, ESP inhibited the adsorption of purified extracellular beta -glucosidases to the cell wall fraction and extracted them from it. These results indicate that ESP plays important roles in the stability and localization of extracellular beta -glucosidases. ESP from A. kawachii directly binds to the enzymes and releases them to the medium from the cell wall layer and then stabilizes them.